posted on 2012-03-08, 00:00authored byAnna Lee, Aftab Ahmed, Diego
P. dos Santos, Neil Coombs, Jai Il Park, Reuven Gordon, Alexandre G. Brolo, Eugenia Kumacheva
It is generally expected that aggregates of metal nanoparticles
are more efficient surface-enhanced Raman scattering (SERS) probes
than individual nanoparticles, due to the enhancement of the electric
field in the interparticle gaps. We show that, for asymmetric nanoparticles,
such as gold nanorods (NRs), this is not always the case: the plasmonic
behavior of NRs depends on the mutual orientation of the NRs in the
ensemble. We report the results of experimental studies and theoretical
analysis of the optical properties of clusters of side-by-side assembled
gold NRs. Ensemble-averaged SERS spectroscopy showed a reduction in
SERS intensity. Comprehensive finite-difference time-domain simulations
showed a reduction of electric field intensity as the number of NRs
per cluster increased. This is due to destructive interference as
the radial component of the surface plasmon modes of the NRs in the
cluster interact with each other. The present work expands our understanding
of the configuration-specific optical behavior of asymmetric gold
nanoparticles. Furthermore, it offers guidance toward the “design
rules” for the development of colloidal NR systems for sensing
applications.